1. Place chopped chiles, lemongrass paste, cilantro, coriander and cumin seed, and salt in a food processor. Zest lime; add. Puree until smooth, adding water a tablespoon at a time if necessary; set aside. Bring a pan of water to a boil. Add noodles; cook until just tender, about 5 minutes. Drain; set aside in bowl of cold water.

2. Heat oil in a large nonstick skillet over medium heat. Add lemongrass mixture, and cook until fragrant, about 1 minute. Add onion; cook until just softened, 6 to 8 minutes. Add bell pepper; cook until just tender, about 3 minutes. Combine cornstarch with water; add to pan. Add pineapple, mushrooms, and coconut milk; simmer. Add shrimp; cook until pink and opaque. Squeeze juice from lime; stir into mixture. Serve garnished with sliced chiles, if desired.